网上找了个现成的图解:
图片占位:http://www.saybb.net/data/news_img/200909/20090910154037723.jpg
图片占位:http://www.saybb.net/data/news_img/200909/20090910232845331.jpg
图片占位:http://www.saybb.net/data/news_img/200909/20090910232857771.jpg
图片占位:http://www.saybb.net/data/news_img/200909/20090910232910342.jpg
图片占位:http://www.saybb.net/data/news_img/200909/20090910232922119.jpg
图片占位:http://www.saybb.net/data/news_img/200909/20090910232938208.jpg
图片占位:http://www.saybb.net/data/news_img/200909/20090910232949908.jpg
图片占位:http://www.saybb.net/data/news_img/200909/20090910233000596.jpg
图片占位:http://www.saybb.net/data/news_img/200909/20090910233011949.jpg
图片占位:http://www.saybb.net/data/news_img/200909/20090910233022645.jpg
图片占位:http://www.saybb.net/data/news_img/200909/20090910233033145.jpg
图片占位:http://www.saybb.net/data/news_img/200909/20090910233045708.jpg
图片占位:http://www.saybb.net/data/news_img/200909/20090910233100240.jpg